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SB 191 
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U. S. DEPARTMENT OF AGRICULTURE. 
" BUREAU OF PLANT INDUSTRY— BULLETIN NO. 141, PART IV. 

H. T. (iALI.UWAY, chiif of Hur'<iu. 



THE IMPOIITANCE OF BROAD 
BREEDING IN CORK 



G. N. COLLINS, Assistant Botanist. 



IssiEi) Jink 4, 1909. 




WASHINGTON: 



G ( ) ^■ K K \ M V. N r !• K I N T I N « i o 1' I' I ( ' K. 



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CONTENTS 



Page. 

Introduction 33 

Development of the present methods of corn breeding 34 

Uniformity not essential in corn 36 

Confusion regarding the term uniformity 36 

Cultural tendencies toward inbreeding 37 

The elimination of "barren stalks" 41 

Continuous improvement through selection 41 

Sunuiiary 42 

HI— IV in 



IS. p. I.— 4fi.S. 



THE IMPORTANCE OF BROAD BREEDING 
■ IN CORN. 



By G. N. Collins, Assistant Botanist. 



INTRODUCTION. 

A stud}' of the primitive types of corn and the histor}' of the more 
productive varieties affords many indications, that the improvement 
of our varieties is being checked by the injurious effects of inbreed- 
ing and that a further advance can best be secured by more fully 
satisfying the natural requirement of cross-fertilization. The con- 
spicuous increase in yield that results from the crossing of distinct 
varieties and the rapid deterioration that follows self-pollination 
strongly support this view. Unfortunately the more recent changes in 
the methods of breeders have not been in the direction of better pro- 
vision for cross-fertilization, but toward a still closer approach to 
self-pollination, the attempt being made to apply to corn theories and 
methods derived from plants naturally adapted for self-fertilization. 

Until recently, the study of evolution and heredity has had little 
effect on the methods employed by breeders of domesticated plants 
and animals. Imf)roved varieties were developed before Darwin's 
time in much the same way that they have been since. "Whether the 
doctrines of Darwin or those of Lamarck, Naegeli. Weismann, or 
Cope should be accepted as giving correct interpretations has seemed 
to be a purely academic question from the standpoint of the practical 
breeder. 

It is entirely different with the recently elaborated theory of De 
Vries. Converts to this new hypothesis liave not l)een slow to claim 
that it has an im])ortant practical bearing, especially when taken in 
connection with tlie facts of Mendelism. Serious changes in the 
methods of breeding are being urged that ai'e likely to have very 
injurious effects if they are generally applied to our varieties of 
Indian corn. 

The definite mechanical character of these theories and the facility 

with which they api)ear to explain some of the facts of heredity 

render them very convincing. There is a tendency to forget their 

limitations and overlook the fact that whatever their value with 

141— IV 33 



34 THE IMPORTANCE OF BEOAD BKEEDING IN CORN. 

close-fertilized j^lants like wheat they are entirely inaiDj)licable to a 
cross-fertilized plant like corn. 

The popularization of the neAv theories has continued until they 
are now not only urged as a basis for scientific experiments in breed- 
ing, but are even recommended as a guide for the practical farmer. 
It is assumed that uniformity is a normal condition. New " ele- 
mentary' species " are supposed to originate by sudden changes and 
then to remain uniform, so that no further change is jDOSsible after 
a " pure strain " has been isolated, until new mutations occur. If 
these theories were correct, then it would be true, as De Yries main- 
tains, that the breeder is wasting time in attempting to ameliorate 
varieties by the continued selection of minute variations after the 
elementary species have been isolated. 

The hundreds of improved forms of domesticated plants which 
have been derived and maintained by. continuous selection through 
long periods of time sufficiently refute the claim that selection is 
ineffective and should warn breeders from the danger of abandoning 
too soon a system which has yielded such brilliant results. As 
applied to corn the De Vriesian doctrine is particularly dangerous, 
since it would replace the already close selection by a method of still 
narrower breeding, the nearest ai:>proach to self-fertilization that is 
possible with a cross-pollinated plant. 

Independent of these theories, many corn breeders have been aim- 
ing at uniformity, and such will doubtless welcome this apparent 
justification. It is perhaps fortunate for the progress of corn breed- 
ing that the wide promulgation of these theories has been delayed 
until the fallacy of the system of close breeding is beginning to be 
ajopreciated and the more thoughtful and observant of our corn breed- 
ers are viewing with distrust the system of close selection and are 
casting about for an alternative method. 

DEVELOPMENT OF THE PRESENT METHODS OF CORN BREEDING. 

Stated broadly, the object of breeding field corn is to produce 
varieties that will give the largest yield of grain under given condi- 
tions. The latitude allowed by this simple object gives the corn 
breeder an advantage over the breeder of more specialized crops — 
an advantage which has not been fully appreciated. The varieties 
of sweet corn fall more nearly in the class with vegetables, and the 
many special requirements, such as taste, appearance, and uniformity 
make their improvement a much more complicated and very different 
l)roblem from that of the improvement of field corn. With field 
corn the development of varieties with special qualities will not 
become an important consideration until the possibilities of corn as a 
human food are much more fully appreciated than at present. 

141— IV 



THE IMPORTANCE OF BROAD BREEDTKG IN CORN. 35 

In the early stages of corn breeding it was thought sufficient to 
select the largest and best-filled ears for seed. With the idea that 
like produces like, this was obviousl}' the way to increase the size of 
the ear. It was soon found that some of the plants that produced 
large ears had undesirable characteristics and selection was moved 
from the crib to the field. 

The next stage was reached when it was realized that, though the 
ear was large and well filled and the plant had no objectionable fea- 
tures, some of the plants failed to reproduce their desirable character- 
istics in subsequent generations. The finest plants are sometimes due 
to particularh?- favorable locations in the field rather than to inher- 
ent superiority. This led to the study of the behavior of the progeny 
of i^articular ears before deciding whether they Avere worthy of 
being used as the foundation of new varieties, and the so-called 
'* ear to row '' method of selection was developed. These more labori- 
ous methods of breeding have all operated to limit the number of 
individuals tested and to restrict the crossing. 

The increased jdelds which follow an intelligent application of this 
method of selection when applied to an unimproved stock have caused 
two important factors to be largely overlooked: (1) The number of 
plants from which careful selection can be made by any one person 
is reduced from thousands to hundreds with a correspondingly re- 
duced chance of securing the individuals really superior as breeders; 
(2) these methods restrict the free crossing that is normal to the 
species, unless accompanied by the extremely laborious method of 
hand-pollination, which still further reduces opportunity of selection 
and renders the method inadequate, except where experiments are 
conducted on a very large scale, beyond the reach of the average 
farmer. 

It has long been known that self-pollinated ears yield ]ilants of 
greatly reduced vigor, and that a few generations of self-j)oHi nation 
usually result in sterility. Yet in spite of this obvious danger sign, 
nearl}' all of our corn breeders have continued to produce varieties 
with the narroAvest possible foundation, often by using a single ear 
as the basis of the new variety and taking measures to prevent the 
bi'inging in of any new strains for fear of contamination. 

Had corn breeding developed independently the danger fi'om nar- 
row breeding would doubtless have been more fidly appreciated, but 
modern corn-breeding methods have been largely adajited from meth- 
ods that have proved successful with otlier crops, siu-h as wheat, oats, 
and barley, in which self-pollination is the rule. AVith self- fertilized 
species it is as safe to start a variety from a single i)lant as it is 
to start a variety of apples from a single bud. Furthermore, these 
autogamous strains tend to show great varietal uniformity, and the 

141— IV 



36 THE IMPORTANCE OF BROAD BREEDING IN CORN. 

degree of this uniformity is regarded as the measure of the purity 
of the strain. With corn, conditions are different. It is normally 
interbred and normally exhibits considerable diversity in conspicuous 
characteristics — diversities difficult to suppress even when the closest 
selection is practiced. 

UNIFORMITY NOT ESSENTIAL IN CORN. 

In the cultivation of many plants varietal uniformity is a prime 
requisite, and with plants Avhere seed is not the part for which the 
crop is grown this uniformity may be secured by narrow inbreeding 
and narrow selection, without imminent danger of deterioration. 
With many plants a reduction in the quantity of seed or in its germi- 
nating power is of relatively small importance. Close breeding may 
be necessary and permissible in such crops as beets, cabbage, lettuce, 
or tobacco, where uniformity in vegetative characteristics is required. 
It may be profitable to j^roduce uniform varieties of chickens, dogs, 
or ornamental plants, even though such varieties may be short lived. 
But the fancier's methods are not applicable to field crops. The corn 
grower receives a relatively small part of his profits in the form of 
prizes awarded on the score-card method of " point ratings," yet, 
except for the seedsman, this is the only monetary advantage in pro- 
ducing corn with perfectly uniform ears. That a corn planter should 
occasionally drop four or five grains instead of three in a hill is about 
the only reason that can be given for insisting upon uniformity in 
shape and size of kernels, and an occasional white speck in the yellow 
corn meal is advanced as sufficient warrant for the careful elimina- 
tion from yellow varieties of all ears with white cobs. The desire 
for uniformity does not always have even these excuses. It is even 
urged by some breeders that the tassels and silk must be uniform in 
color, that the ears must be uniform in shape, with a fixed number 
of grains to the inch. There is not even a fancied pecuniary ad- 
vantage in this, but it is held that diversity in even these unessential 
characteristics stamps a variety as mongrel and therefore undesirable. 

Even the universal insistence upon large ears may not always be 
advisable, for it has resulted in the development of plants bearing 
single ears instead of the two or more ears that are normal to the 
species. Where the season is short the limitation to a single ear is a 
decided advantage, but under other conditions a plant producing two 
or three ears of moderate size may yield a quantity of shelled corn 
that sufficiently exceeds that on a single large ear to more than offset 
the additional cost of harvesting. 

CONFUSION REGARDING THE TERM UNIFORMITY. 

A misunderstanding regarding the meaning of the term uniform- 
ity has done much to s]-)read the practice of inbreeding and has 

141 — IV 



THE IMPORTANCE OF BROAD BREEDING IN CORN. 37 

worked great injury to the cause of corn improvement. To t\io few 
successful breeders who have produced varieties of lasting value 
uniformity has not signified an identity of measurable characters, 
but is a kind of similarity of exi)ression, so to speak, by which the 
breeder recognizes a family resemblance, much as we recognize the 
relatives of our intimate friends, although at a loss to indicate 
wherein the resemblance lies. Thus to an experienced breeder two 
ears of corn, with measurable characters that coincide as closely as 
possible, will immediately be recognized as belonging to different 
types. The ears and grains may be of the same size and shape, the 
color and indentation the same, yet to the practical breeder the two 
ears would appear to be lacking in uniformity. Conversely, ears 
which are obviously dissimilar in these particulars will promptly be 
recognized as belonging to the same strain. 

The score card Avas an attempt to reduce this intimate and almost 
intuitive knowledge of the practical breeder to an exact science for 
wider application, but it has proved a lamentable failure — lamentable 
because it gave rise to the idea that the uniformity of score-card 
ratings was the kind of uniformity which successful breeders con- 
sidered essential to valuable strains of corn, and because uniformity 
in score-card ratings can only be secured by rigid inbreeding. 

CULTURAL TENDENCIES TOWARD INBREEDING. 

The cultivation of corn is of very great antiquity in America, and 
the cultural operations to which it has been subjected from the earli- 
est periods have ditfered radically from those applied to other crops. 
With primitive peo])le the seed of other cereals is unavoidably^ mixed 
in planting, but corn is usually stored on the cob and the ears used 
for seed are carried into the fields at the time of planting, and the 
kernels shelled off as they are to be drojiped into the ground. Thus 
the plants from the same parent ear grow up together, and with 
most primitive tribes, though the plantings may be considerable in the 
aggregate, the individual fields are in most cases so small that one 
or two ears will often suffice for the entire field. The opportunity 
for crossing is thus very slight. It would be natural for even the 
most primitive man to select for seed the largest ears or those that 
particularly caught his fancy, and the same tyjie would be selected 
year after year. The seed ears also figure in many religious cere- 
monies, which no doubt tends to the establishment of definite standards 
of selection. 

It is universally believed by the Indians of Central America that 
the varieties of corn in each locality are best adaj)ted to that locality, 
and that other varieties brought in from other regions never yield 
so well. That this belief is well founded has been demonstrated by 

141— IV 



38 THE IMPORTANCE OF BROAD BREEDING IN CORN. 

the numerous exjierinients of P^uropean settlers in tropical America, 
Avho are prone to regard as superstition this native belief and to 
import improved varieties from more or less distant localities. The 
failure is usually so complete the first 3'ear that the experiment is 
abandoned. This abnormal behavior of corn under new conditions 
intensifies the close breeding, and the close breeding in turn operates 
against the interchauge of varieties by making the adjustments to 
the particular environment more delicate. That these primitive 
systems of breeding have not been indiscriminate is shown by the 
great number of well-defined types that exist among the American 
jiborigines. 

Among a number of primitive tribes where the cultivation of corn 
has reached a high state of development, the injurious effect of this 
close breeding appears to have been recognized, since they have meth- 
ods of guarding against it. Thus the Indians in the region of Que- 
zaltenango, in western Guatemala, and the Hopi Indians of Arizona 
make a regular practice of placing seeds of more than one local 
A'ariety in each hill, with the idea that larger yields can be obtained 
in this wa}'. 

The very general fact that the immediate effect of crossing two 
closely bred strains is to increase the vigor is well exemplified in corn. 
Although this increased vigor of first-generation hybrids is well 
recognized by many practical corn breeders, the value of the fact has 
been largely obscured by the idea that the hybrid must be considered 
as a new variety and that uniformity must be secured before the 
results could have general application. To attem])t to establish uni- 
formity by a new course of selective inbreeding is to sacrifice the 
vigor gained by crossing. 

Attention has been so persistently centered on the production of 
new and uniform strains that the yield and vigor of the first genera- 
tion of hybrid plants as compared with the parents is seldom reported. 
In all the cases that have come to our attention the yield of the 
hybrid has been in excess of the average of the parents. Five cases 
reported b}^ Morrow and Gardner," of the Illinois Agricultural Ex- 
periment Station, gave increases over the average of the parents 
running from 1.9 per cent to 28 per cent, with an average increase of 
14 per cent. McClure,^ of the same station, also reports on 12 differ- 
ent hybrids of sweet, pop, soft, and flint varieties; 10 showed an 
increase in the weight of the ear in the first generation over the 
average of the parents, and one of the exceptions is exjolained by the 
author as being due to unfavorable situation, the decrease in the 

":\rorrow, G. E., and Gardner, F. D. Bulletin 2r^, Illinois Agricultural Exper- 
iment Station, p. 179. 1S93. 

*McCliu-e, (;. \Y. Bulletin 21, Illinois Agricultural Experiment Station, p. 82. 
1892. 

141— IV 



THE IMPORTANCE OF BROAD BREEDING IN CORN. 39 

other case being 4.G per cent, while the average increase for the Avhole 
series of 1:2 crosses is lO per cent. runnin<2: as high as 52.8 per cent. 

If similar increases had been secured by any change in cultural 
methods, experiments to determine the range of applicability of the 
new method would have been i)romptly inaugurated and the true 
value of the facts ascertained. Although the fact has long been 
established that significant increases can be secured by crossing, we 
are still Avithout knowledge regarding the conditions necessary for 
this increase. It is to be expected that the increase Avill be greatest 
between strains that liaA^e been closely selected, but there is no direct 
evidence on this point. ^Ve should also lose no time in securing 
information regarding the amount of difference that should exist 
between the strains crossed to secure the maximum increase of vigor. 
There is a wide and almost untouched field in this direction that Avill 
require an enormous amount of experiment and observation before 
justice will have been accorded to this possibility. 

The definite and well-known facts that self-fertilization of corn 
inevitably leads to sterility and that the jaeld can be increased by 
the crossing of varieties have not been sufficient to attract attention to 
the dangers of inbreeding and close selection. Xo middle course 
l^etween the indiscriminate planting of the general run of seed and 
the rigid selection of a definite type seems to have been seriously 
considered. Had it been realized that diversity is as necessary to the 
life of the species as is chloroj^hyll to the life of the individual plant, 
it would have been evident that one might as well breed to eliminate 
the green color from the leaves as to suppress this normal variation. 
From a consideration of the habits of the jilant the course suggested 
in undertaking the improvement of corn would be to seek the best 
methods for continuing to combine distinct strains, thus utilizing 
the increased vigor and i^roductiveness resulting from their inter- 
breeding. 

While the crossing of our more or less inbred varieties may confi- 
dently be expected to result in increased vigor and fertilit}', it is 
hardly to be expected that the full amount of the increase in yield 
that follows such crossing can l)e maintained in future generations. 
The probability is that a part of the increased fertilitj^ of the hy- 
brids will prove to be confined to the conjugate generation; that is, to 
the generation innnediately following the crossing. In this genera- 
tion male and female elements, representing the two parent varieties, 
are present in the nuclei of the plant, but hav^ not completed the 
process of conjugation, with the result that a sort of protoplasmic 
tension exists, in some way associated with increased vegetative and 
reproductive activity." There is good reason to believe that this is 

"Cook, O. F., and Swingle, W. T. Evolution of Cellular Structures. Bulletin 
81, Bureau of Plant ludustry. V. S. Dei'artuicnt of Agriculture. 1905. 
141— :v 



40 THE IMPORTANCE OF BROAD BREEDING IN CORN. 

the case in certain cotton hybrids, and if it should also prove to be 
an important factor in the increased yields of corn hybrids the 
results would warrant the production of hybrid seed in a breeding 
plot each year for field planting the following- year. To secure 
hybrid seed it would only be necessary to plant two distinct varieties 
in alternate rows, detasseling one variety and using the seed from 
the detasseled variety for the next year's general planting. Seed 
from the variety that was not detasseled would not be mixed and 
selections could be made to supply the breeding plot for the two 
following years. By detasseling the other variety in the next year a 
stock of pure seed of this also could be grown. By this system of 
alternation pure stocks of seed of the two varieties could be main- 
tained. There would be produced every year a stock of hybrid seed 
for the field planting of the next year and a stock of pure seed of one 
of the varieties for planting the seed plots of the two following years. 

The same result could be approximated by planting in the same 
waj' and detasseling one of the varieties in one half of the field and 
the other variety in the other half of the field. By this method 
seed of both the varieties would be secured each year, but there 
would be considerable indiscriminate crossing. 

The fact that corn is wind-pollinated makes the continual pro- 
duction of conjugate or first -generation hybrids on a commercial 
scale immensely more practicable with corn than with any other 
field crop. 

In still another way the artificial crossing of two varieties may be 
expected to increase the yield. "With such hybrids none of the seed 
is self -pollinated, while with the crop grown in the usual way the 
percentage of self-fertilized grain must be very considerable. In 
most of our varieties the natural proterandrous tendency of corn has 
been reduced, until under ordinary climatic conditions the pollen of 
nearlv every plant is still being shed when the silks become receptive. 
Unless the w ind is blowing when the pollen is shed a large amount 
of self-pollination is inevitable. It is to be expected, therefore, that 
au}?^ method of treatment that Avould eliminate or reduce this self- 
pollination would result in an increase of the vigor and yield of the 
resulting corn plants, even Avithout hybridization. The use of detas- 
seled plants for the production of seed may thus be found worth 
while, quite apart from the question whether detasseled plants them- 
selves yield more than those that are not detasseled. 

Whatever may be the true explanation of the increased fertility of 
hybrid corn plants, the fact remains that larger yields of corn can 
be secured in this w^ay. The study of the methods by w*hich these 
important factors can l)e made most effective should at least receive 
a place by the side of the study of elementary sj^ecies and the quest 
of uniformity. 

141— IV 



THE IMPORTANCE OF BROAD BREEDING IN CORN. 41 

THE ELIMINATION OF " BARBEN STALKS." 

Another factor which has worked toward the inbreeding and con- 
sequent deterioration of highly bred varieties of corn is the removal 
of the so-called '' barren stalks." The elimination of nonproductive 
plants is undoubtedly desirable, but the removal of barren stalks as 
usually practiced is not a step in this direction. A truly barren stalk 
is one that fails to produce seed. So far as the seed is concerued, 
therefore, this elimination is automatic and inevitable, but it has been 
urged that the barren stalks must be removed before they produce 
pollen, on the theory that pollen from barren stalks is likely to cause 
deterioration in the progeny of neighboring plants. AVhere this 
practice is folloAved it results onh' in the detasseling of all proteran- 
drous plants, for, as pointed out by Soule and Vanatter," it is impos- 
sible to distinguish the trul}^ barren plants at the time of tasseling. 
"With many varieties, especially those which have not been subjected 
to rigid selection, some of the plants which eventually prove to be 
the most prolific show only small rudiments of ears at the time of 
tasseling. The continued removal of such plants results not in the 
elimination of barren stalks, but in the elimination of the plants 
which possess a valuable adaptation to avoid self-pollination. This 
weeding out of the more proterandrous individuals has been continued 
with some varieties until the majority of the j)lants i)roduce staminate 
and pistillate flowers at the same time. When these varieties flower 
in comparatively still weather, there must be a large i)ro|)ortiou of 
self-pollinated seed and a consequent weakening of the variety. This 
persistent tendency to proterandry can be thought of as a natural 
reaction of the species against the danger of extinction from inbreed- 
ing. Even the true barren stalks might represent a tendency on the 
part of the plant to become dioecious. In localities with very short 
seasons it may be well to discriminate against the tendency in the 
plant to put out ears too long after the tassel has matured, but 
elsewhere the avoidance of self-pollination is more important. 

CONTINUOUS IMPROVEMENT THROUGH SELECTION. 

The fact that narrow breeding in corn results in a reduction of 
vigor has remained unappreciated largely because narrow breeding 
is always accompanied by selection for yield and vigor. The two 
processes are opposed, so that movement in either direction is masked 
and counteracted. Varieties thus produced are delicately adapted 
to the exact conditions under which they have been selected, and often 
show marked deterioration when placed under new conditions. The 
very delicacy of the adjustment helps to insure the much desired 



« Bulletin 1G5, Virginia Agricultural Exijeriuieut Slatiou. 

141— IV 



42 THE IMPORTANCE OF BROAD BREEDING IN CORN. 

Liniformit}', for Avitli any change of characters the debilit}' of the 
stock becomes more manifest and the elimination of the variant indi- 
viduals is certain. Increased yields are obtained by making the 
yield of the individual plants more uniform, even when the full pos- 
sibilities of i^roduction are not approached. The best plants of a 
highly bred variety are not conspicuously more prolific than the best 
individuals in fields from unselected seed.'^ 

This failure of varieties to continue to improve in vigor and 
fertility under continuous selection gives apparent support to the 
idea of De Vries that the initial selection of '' pure strains " is the 
only progress that can be expected. It has already been seen that 
attempts to secure increased vigor by close selection are impeded by 
the weakening effects of inbreeding. When selection is not ham- 
pered in this way, but is directed to characters not dependent on 
vigor and fertility, and consequently not affected by inbreeding, 
continuous progress may be made. Thus in the selections made by 
Hopkins for high and low^ protein content, rapid and continuous 
progress was made and an extreme was reached far in excess of 
anything observed in the original sample. The last reports show 
that the plants were no more uniform with respect to these characters 
than at the beginning of the experiment.* 

Though necessarily impeded by inbreeding, important advances 
in yield have been made by means of close selection, but the value 
of these improvements should not be allowed to obscure the fact that 
the full possibilities of production are not reached until the incre- 
ment of vigor obtained by crossing has been added. Even if the 
yields obtainable by crossing w^ere not larger than those to be secured 
by persistent close selection, it is easier to permit crossing than it is 
to provide the very careful and skillful selection required to maintain 
high yields without crossing. To use crossing as a means of sustain- 
ing fertility, instead of relying ujDon selection alone, would also keep 
our stocks in more normal physiological condition, more resistant to 
disease, and less liable to injury by adverse conditions. 

SUMMARY. 

The development of the present methods of corn breeding has re- 
sulted in greatly limiting the number of individuals that serve as a 
foundation for improved strains. The danger of this course, as 

" It has recently been pointed out by Mr. O. F. Cook that the apparent ad- 
vantage of selection is greatest in degenerating stocks. See Bulletin 146, Bureau 
of Plant Industry, F. S. Department of Agriculture. " The Superiority of Line 
Breeding Over Narrow Bi*eeding." 

* Smith, L. H. Ten Generations of Corn Breeding. Bulletin 128, Illinois 
Agricultural Experiment Station. 1908. 
141— IV 



THE IMPORTANCE OF BROAD BREEDING IN CORN. 43 

shown b}"- the sterility of self-pollinated plants, has been unheeded, 
largely because theories and methods have been carried over to corn 
from other crops which are normally self-iooUinated or where a high 
degree of uniformity is essential. 

Great uniformity is of little or no economic value in corn varieties, 
and since it can be acquired only through close breeding it is actually 
undesirable to the grower. The natural requirements of cross- pollina- 
tion make the problem of corn improvement entirely different from 
that of most of our cultivated plants. 

Selection for increased 3'ield with the maximum instead of the 
minimum of cross-breeding seems never to have been tried as a scien- 
tific experiment. On the other hand, the farmers of our corn-grow- 
ing regions have practiced a system of broad breeding by choosing 
many ears from widely scattered plants in large fields and mixing the 
shelled corn before planting. ]Much of the basic improvement of our 
corn varieties may be ascribed to this system of increasing and main- 
taining vigor and fertility. 

An effort to reduce the intimate intuitive knowledge of the successful 
breeder to measurable characters has led to the development of the score 
card. Instead of accomplishing the desired result, the score card 
has operated to intensify the closeness of selection, since uniformity 
in formal characters can be secured only by close breeding. 

Although the methods that obtain among the primitive tribes of 
corn-growing Indians indicate that corn has been subjected to narrow 
breeding from remote times, the more intensive form of narrow 
breeding has been practiced for little more than a decade, yet the 
debilitating effects of this method are becoming apparent. 

That corn is benefited by additional crossing, even when grown by 
primitive methods, is indicated by the custom which some tribes 
have of regularly mixing distinct strains to increase the yield. 

It is abundantly demonstrated that the crossing of distinct varieties 
gives increased yields." With the idea that only uniform varieties 
could be of value the practical importance of this fact has been over- 
looked and the gain has been limited by subsequent inbreeding of the 

"After this report was submitted in January, 1909, au article appeared by Dr. 
E. M. East, of the Connecticut Agricultural Experiment Station (see American 
Naturalist for March, 1909), describing additional instances of increased yields 
of corn hybrids. Thirty different crosses between varieties were grown in 
comparison with the parent varieties, with the result that " In every case an 
increase in vigor over the parents was shown by the crosses." In the four 
cases in which the yields were measured the product of the hybrid exceeded 
that of either parent, the increase of the hybrids over the parents averaging 
77 per cent. Doctor East also considers the practicability of i)roduciiig hybrid 
seed for commercial plantings and outlines a method practically identical with 
that suggested here. 
141— IV 



44 



THE IMPORTANCE OF BROAD BREEDING IN CORN. 



hybrids. Should the increased yield of In'brid plants prove to be 
greatest in the first generation or should the complete elimination of 
self-fertilization prove an important factor, it is quite practicable to 
maintain a continuous supply of hybrid or cross-pollinated seed. 

A study of the habits of the plant from the standpoint of cross- 
fertilization makes apparent the nature of the so-called "barren 
stalks,"' which may be thought of as an adaptation to avoid self- 
pollination. The elimination of these proterandrous plants results 
in increasing the percentage of self-pollinated plants and is a prac- 
tice of doubtful value. 

The ill effects of inbreeding and selection for increased yield and 
vigor have tended to neutralize each other, and the consequent lack 
of continued improvement has lent color to the idea that continuous 
selection is ineffective. With characters that are not affected by 
decreased vigor continuous advance has been made by selection. 

141— IV 



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